[www-scripts] Clang Attribute Doc Update: ERROR

[root via www-scripts]

UPDATING LLVM SOURCES
HEAD is now at 3b8d895 SourceManager: Remove a redundant nullptr check in getNonBuiltinFilenameForID, NFC
>From https://github.com/llvm/llvm-project
 * branch            master     -> FETCH_HEAD
   3b8d895..4437df8  master     -> origin/master
First, rewinding head to replay your work on top of it...
Fast-forwarded master to 4437df8eedfdaa11b445c34fc3b19a1b14cb3d93.
CMake Error at CMakeLists.txt:3 (cmake_minimum_required):
  CMake 3.13.4 or higher is required.  You are running version 3.7.1


-- Configuring incomplete, errors occurred!